The present invention relates to a diaphragm type actuator, and more particularly to a diaphragm breakage condition detecting device for a pressure control device.
In general, with a conventional diaphragm type actuator, it is impossible to directly detect breakage in the diaphragm member. It is only possible to indirectly detect the breakage in the diaphragm member in accordance with a phenomenon appeared in the event that there occurs breakage in the diaphragm member whereby the actuator becomes out of order.
Referring to FIG. 1, there is shown an internal combustion engine 10 with a turbo charger. There is provided an air valve 12 in an intake passage 14 connected to an intake manifold 16 of the engine 10. In order to constitute a turbo charger designated by reference numeral 30, there are provided a blower 32 of a compressor in the entrance of the intake passage 14 and a turbine 34 in an exhaust passage 20 connected to the exit of an exhaust manifold 18, wherein the blower 32 is directly connected to the turbine 34 by a shaft 36 so as to rotate simultaneously.
Reference numeral 22 denotes a bypass passage provided so as to bypass the exhaust passage 20, whereby a part of exhaust air is conducted through the bypass passage 22.
In order to control the amount of exhaust air through the bypass passage 22, there is provided an exhaust bypass valve 24 actuated by a diaphragm type actuator 40. The conventional diaphragm type actuator 40 comprises a casing 42, a diaphragm member 44 partitioning the casing 42 into a first chamber 46 and a second chamber 48 exposed to air, an actuating rod 50 the one end of which is mounted on the diaphragm member 44 while the other end thereof is connected to the exhaust bypass valve 24, and a compression spring 50 disposed between the diaphragm member 44 and the inner wall of the casing 10.
As seen from FIG. 1, the diaphragm type actuator is constituted so that an output pressure P.sub.1 at the exit of the compressor 32 is supplied to the first chamber 46.
In operation, when the pressure P.sub.1 at the exit of the compressor 32 is below the predetermined value prescribed by the normal operation of the turbo charger 30, the diaphragm member 44 is held at the initial position or moves in the right direction thereof depending on the pressure differentials between the output pressure P.sub.1 and the repulsive force of the compression spring 52. Thereby, the exhaust bypass valve 24 provided in the bypass passage 22 opens in accordance with the pressure differentials. Thus, the diaphragm type actuator makes it possible to suppress the output pressure P.sub.1 at the exit portion of the blower 32 so as not to exceed the upper value, such as, about 1.5 atomospheric pressure. Thereby, it is possible to prevent the excessive rotation of the turbo charger.
Meanwhile, the exhaust temperature is very high, such as 700.degree.-800.degree. C. Accordingly, with the diaphragm type actuator 40 shown in FIG. 1, the diaphragm 44 usually made of rubber is apt to be broken because of heat conducting through the actuating rod 50.
In the event that there occurs breakage in the diaphragm 44, the pressure of the first chamber 46 filled with a high pressure is lowered, the exhaust bypass valve 24 is held at the closed position. As a result, this makes it impossible to regulate the pressure P.sub.1 at the exit portion of the compressor 32. Thereby, it becomes impossible to prevent the excessive rotation of the turbo-charger 30.
In the prior art, in order to determine the occurence of the above inconvenience, an attempt is made to provide a pressure meter for indicating the pressure P.sub.1 at the exit of the compressor, and/or alarm lamp or an alarm buzzer for alarming the excessive elevation of the pressure sensed by the pressure meter.
However, with this attempt, it is impossible to detect the breakage in the diaphragm until the pressure P.sub.1 at the exit of the compressor 32 excessively elevates. Accordingly, it is impossible to prevent damage or breakage in the internal combustion engine or turbo-charger prior to occurrence of the same. Further, it is also impossible to precisely judge the cause of the excessive elevation of the pressure.
In view of this, another attempt is made to provide a safety valve at the exit of the compressor, thereby, when the pressure is excessively elevates, to feedback a part of air at the exit of the compressor to the entrance of the compressor or let the same being escaped from an opening exposed to air.
However, if this attempt is applied to an internal combustion engine in which a carburetor is provided upstream of the compressor, a mixture being supplied from the carburetor is emitted to the atomosphere through the safety valve. As a result, this may produce the atomospheric pollution, the varitation of air/fuel ratio, and poor fuel economy. Accordingly, if this attempt is applied to the internal combustion engine in which a carburetor is provided upstream of the compressor, there remains drawback that the turbo-charger is injured or damaged.